This invention relates to calculating devices such as hand-held calculators and computers. More particularly, this invention relates to method and apparatus for accessing and selecting any function in the calculating device in two keystrokes.
Prior calculators and other devices that have dedicated function keys have faced a dilemma. As these devices have progressed, they have offered more functions on a limited number of keys. Each key is thus used for several functions, typically up to four per key. A multi-function key may have a primary function, i.e., the function executed by simply pressing the key, as well as a number of secondary, shifted functions. The shifting may be accomplished in a number of way. A common technique is key-based shifting, where a shift key is pressed prior to pressing the function key. Another technique is time-based shifting, where a multi-function key is pressed until the desired function is indicated and the key is then released to execute the function. A third technique is pattern-based, where the number of key presses within a predetermined time period determines which function is executed.
These shifting techniques have allowed more functions to be added to a key, but the increased functions have made use of the keys increasingly difficult. The symbols representing the key's functions must be somehow placed about the key and recognized by the user as to how they are reached. For example, in U.S. Pat. No. 4,202,038, the key's functions are placed directly on the key face. This requires, however, that the keys be relatively large and limited in number. Therefore, as a practical matter, the number of symbols that can be placed adjacent a key is about four.
Limiting the number of functions a calculating may perform, however, may unacceptably limit the performance of the device. More keys may be added, but this requires either a larger keyboard (limiting portability) or smaller keys (limiting ease of use).
The present invention offers an alternative whereby the functions associated with a key are not limited to those that can be displayed adjacent to the key, and yet each key function can be executed with no more than two key presses.